1. Field of the Invention
The invention relates to cholesteric liquid crystal display (LCD) devices, and in particular to color cholesteric liquid crystal display devices and driving methods for writing images therein.
2. Description of the Related Art
Liquid crystal display (LCD) devices have many advantages over other display devices such as having a smaller volume, lighter weight and lower power consumption, and are applicable in a variety of electronic and communication devices, including notebook computers, personal digital assistants (PDA), mobile phones and the like due to its lighter weight, thinner profile, and portability.
Conventional liquid crystal displays integrated with touch control panels are typically applied in notebooks or personal computers, and particularly to personal assistants (PDA). Some liquid crystal display devices are integrated with a position sensing touch control panel. When a stylus touches the liquid crystal display device and makes contact, the position sensing touch control panel detects the position of the stylus, thereby displaying the position on the liquid crystal display device.
For example, a conventional resistive type touch-sensitive liquid crystal display device comprises an electrical resistive touch panel and a stylus. When the stylus direct contacts the touch panel, location of the stylus on the touch panel is detected according to resistance change of the circuit in the electrical resistive touch panel.
Typically, a touch-sensitive liquid crystal display device integrates a touch control panel on a liquid crystal display (LCD) panel as an input type liquid crystal display device. The touch panel is configured between the viewer and the liquid crystal display (LCD) panel to facilitate hand-writing input. Incident light passing through the touch panel, however, may cause partial reflection, resulting in a glaring light for the viewer and a detrimental image contrast ratio for the LCD panel.
In order to solve the glaring light problem and deteriorating image contrast ratio for the LCD panel, U.S. Pat. No. 6,982,432, the entirety of which is hereby incorporated by reference discloses a touch-sensitive liquid crystal display device including a combined tough panel and LCD panel in which the LCD panel is configured between the viewer and the touch panel to facilitate hand-writing input.
FIG. 1 is a cross section of a conventional touch-sensitive liquid crystal display device. Referring to FIG. 1, a conventional touch-sensitive liquid crystal display device includes a touch control panel 4 and an LCD panel 3A in which the LCD panel 3A is configured between the viewer and the touch control panel 4. The LCD panel 3A includes a color filter substrate 31 with an electrode layer 32 thereon and a transparent substrate 35 with a transparent electrode layer thereon. A micro-molecule dispersed liquid crystal layer 33 is interposed and enclosed by a sealer 33 between the color filter substrate 31 and the transparent substrate 36.
The touch control panel 4 includes an electrode 41 disposed on the transparent substrate 36 and an electrode 43 disposed on the substrate 44. The electrode 41 and the electrode 43 are separated by a gap. The transparent substrate 36 and the substrate 44 are sealed by a sealer 42. Be exerting pressure F from the stylus which passes to the electrodes 42 and 43 of the touch control panel 4, the location which the electrodes 42 and 43 are contacted is determined as the stylus position. Hand-writing input and displaying of images are respectively achieved via the touch control panel and the LCD panel. The touch-sensitive liquid crystal display device comprises at least two layers of independent panel structures. The entire structure and fabrication process is complex, resulting in high production costs.
Further, U.S. Pat. No. 6,392,725, the entirety of which is hereby incorporated by reference discloses a color cholesteric liquid crystal display device. The color cholesteric liquid crystal display device includes a stacked structure of three different single-color cholesteric liquid crystal layers which is configured with a pair of writing electrodes disposed thereon. An applied voltage is used to control writing images on the color cholesteric liquid crystal display device.
FIG. 2 is a cross section of a conventional three-layered stacked cholesteric liquid crystal display device. Referring to FIG. 2, a conventional handwriting type cholesteric liquid crystal display device includes a stacked cholesteric liquid crystal display panel 50 and a handwriting input device 60. The stacked cholesteric liquid crystal display panel 50 includes a pair of opposing substrates 52 and 53 with three different color liquid crystal layers 58A, 58B, and 58C interposed between the substrates 52 and 53. Separation plates 54 and 55 are respectively interposed adjacent to the liquid crystal layers. Spacers 59A, 59B, and 59C are filled in each liquid crystal layer to maintain a uniform gap therein. An absorption layer 56 is disposed on the back of a lower substrate 53.
The handwriting input device 60 includes a pair of writing electrodes 61 and 62 disposed on an outer side of the stacked cholesteric liquid crystal display panel 50. The handwriting input device 60 is controlled by a controller 11 to input an image. Since the conventional handwriting type cholesteric liquid crystal display device includes a stacked structure with three cholesteric liquid crystal layers, different control voltage waveforms are needed for different cholesteric liquid crystal layers, resulting in high process complexity and high production costs.
In addition, there are other conventional color cholesteric liquid crystal display devices wherein input is from the back of an LCD panel by a photo-input device. Additional light sources, however, are necessary as a light medium. Moreover, an additional light detective layer is also needed, resulting in high structural complexity, usage inconvenience, and high production costs.